馬祖地區淨水場原水藻類有機物特性及三鹵甲烷生成之研究

Abstract

臺灣外島馬祖地區淨水場主要以水庫水作為原水來源，夏季時水庫常面臨藻華現象會使得淨水場操作效率降低，且水場大部分仍以次氯酸鈉(NaOCl)作為主要消毒劑，雖然前加氯程序可降低藻類活性及降解水中DOM以增加後續混凝去除效率，但過程中會破壞藻體細胞而釋出藻類有機物(algogenic organic matter, AOM)，並增加消毒副產物如三鹵甲烷生成之隱憂。然而，AOM的特性會隨著藻種的差異而使得三鹵甲烷生成潛能有所差異。 因此，本研究將探討馬祖地區勝利及儲水沃淨水場含藻原水中AOM的特性及三鹵甲烷生成潛能之關係，先從含藻原水中以掃流超過氯薄膜模組濃縮及分離藻類細胞，再進行破藻使藻體中有機物釋出並萃取配製AOM溶液。再以螢光光譜儀法(EEM)及其搭配粒徑排除層析法(HPSEC)分析AOM之組成成份及分子量特性，接著添加過量NaOCl (五倍DOC)，分析AOM特性變化及其與三鹵甲烷生成潛能之關係。 研究結果顯示，勝利與儲水沃水場優勢藻種分別為縫藻及直鏈藻，其中直鏈藻AOM中類腐植質成份較縫藻高，但兩種原水AOM成份主要均為類蛋白質物質(protein-like substances)，且溶解性有機物(dissolved organic matter, DOM)成份皆為類腐植質物質(humic-like substances)。而AOM中主要成份以類微生物副產物及小分子官能基團(< 100 kDa)為最多，加氯後對類微生物副產物及類黃酸物質之氧化降解程度最大。從螢光光譜法結果顯示類黃酸與類微生物副產物的平均螢光強度比值與三鹵甲烷生成潛能呈現正相關趨勢，顯示其兩者比值可作為馬祖地區含藻原水三鹵甲烷生成潛能之評估指標。另外，在不同的原水中DOM三鹵甲烷生成潛能皆遠高於AOM，因為DOM含有大量的類腐植質成份。而研究進一步發現水中若存在溴離子濃度越高會提高三鹵甲烷生成潛能。

The raw water of waterworks in Matsu area is mostly taken from reservoirs. A large number of algae blooms occur in summer season in reservoirs and lower the operational performance of waterworks. NaOCl oxidant is commonly used in WTPs as a disinfectant to degrade the algae and their metabolites or dissolved organic matter (DOM) for approving efficiency in coagulation and sedimentation. However, pre-chlorination probably induce cell lysis and the release of algogenic organic matter (AOM) from algae to increase in the amounts of disinfection by-products (DBPs), such as trihalomethane (THM). The characteristics of AOM from different algae species strongly affect the formation potential of THM. This study aimed to investigate the relationship between differences on the characteristics of AOM from algae in various raw waters from Shengli and Chushuiwo waterworks in Matsu and the corresponding THM formation potential (THMFP). The algae-laden solution was concentrated by ultrafiltration and then AOM was collected through algae breaking process to a desired dissolved organic carbon concertation as high as 5 mg/L. Excitation-emission matrix fluorescence spectroscopy and high performance liquid chromatography-size exclusion chromatography methods were used to quantify the composition and molecular weight distribution of the AOM. The corresponding THMFP was determined by using excess chlorine dose at a given Cl/DOC ratio (5:1). The results indicated that dominant algae species in Shengli and Chushuiwo are Monoraphidium and Melosira, respectively. The predominant components of AOM and DOM in Shengli and Chushuiwo are protein-like and humic-like substances, respectively. The AOM contains the majority of soluble microbial by-product-like substances with small molecular weight (<100 kDa). After chlorination, the most of SMP substantially degrade. The results of EEM survey suggested that the averaged fluorescence intensity ratio between fulvic acid-like substances and SMP in AOM solution is well-correlated positively with the corresponding THMFP. In addition, the THMFP for DOM in various raw waters was much more than that for AOM because DOM is composed of a large number of humic-like substances. It was found that the quantity of THMFP after chlorination increases with increasing the amounts of bromine ions in raw water.